1. Field of the Invention
The present invention relates to a radiation image storage panel comprising a support and a phosphor layer provided thereon which comprises a stimulable phosphor.
2. Description of the Prior Art
For obtaining a radiation image, there has been conventionally employed a radiography utilizing a combination of a radiographic film having an emulsion layer containing a photosensitive silver salt material and an intensifying screen. As a method replacing the conventional radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor as described, for example, in U.S. Pat. No. 4,239,968, has been recently paid much attention. In the radiation image recording and reproducing method, a radiation image storage panel comprising a stimulable phosphor (i.e., a stimulable phosphor sheet) is used, and the method involves steps of causing the stimulable phosphor of the panel to absorb a radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light and infrared rays (hereinafter referred to as "stimulating rays") to release the radiation energy stored in the phosphor as light emission (stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as visible image from the electric signals.
In the radiation image recording and reproducing method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to an object at considerably smaller dose, as compared with the conventional radiography. Accordingly, this method is of great value especially when the method is used for medical diagnosis.
The radiation image storage panel employed in the radiation image recording and reproducing method has a basic structure comprising a support and a phosphor layer provided on one surface of the support. Further, a transparent film of a polymer material is generally provided on the free surface (surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical shock.
The phosphor layer comprises a binder and a stimulable phosphor dispersed therein. The stimulable phosphor emits light (gives stimulated emission) when excited with an electromagnetic wave such as visible light or infrared rays (stimulating rays) after having been exposed to a radiation such as X-rays. Accordingly, the radiation having passed through an object or having radiated from an object is absorbed by the phosphor layer of the radiation image storage panel in proportion to the applied radiation dose, and a radiation image of the object is produced in the panel in the form of a radiation energy-stored image. The radiation energy-stored image can be released as stimulated emission by sequentially irradiating the panel with stimulating rays. The stimulated emission is then photoelectrically converted to electric signals, so as to reproduce a visible image from the electric signals.
The radiation image recording and reproducing method is generally carried out using a radiation image recording and reading-out apparatus of built-in type which comprises a means (recording means) for recording a radiation image on a radiation image storage panel by exposing the panel to a radiation having image information, a means (read-out means) for reading out the radiation image by irradiating the panel with stimulating rays and photoelectrically detecting stimulated emission given by the panel, a means (erasing means) for erasing a radiation image remaining in the panel by irradiating the panel having been read out with a light for erasure, and a transfer system which connects these means for transferring the panel from one means to another means. Otherwise, the method can be also carried out using apparatus of separate type in which the recording means are separated from the read-out means and the erasing means, that is, using a radiation image recording apparatus (radiographic apparatus) and a radiation image reading-out apparatus having the erasing facility. The panel having been subjected to the erasing procedure in any of the above apparatus can be reused in the next recording, so that the panel is repeatedly used. Especially, a panel is cyclically reused in the former built-in type apparatus.
In these apparatus, the transfer system for conveying the panel to the next processing means is a complicated combination of various transfer members such as a nip roller, a transfer belt and a guide plate. During the transfer, the radiation image storage panel is repeatedly applied with mechanical shocks such as bending and collision with the members. More recently, as the apparatus is miniaturized and the transfer space is necessarily smaller, the panel tends to be transferred in the state of severely bending by the rollers, etc. When the panel is repeatedly used in such apparatus, the phosphor layer of the panel is liable to suffer from cracks, and thereby an image provided by the panel is deteriorated in the image quality.
On the other hand, the radiation image storage panel is required to have stiffness (so-called "nerve") at a certain level or above. For instance, a depot for allowing panels to temporarily stay is sometimes provided on the way of the transfer system (for example, before the read-out means) to adjust the difference of the processing time in each means. In this depot, panels are allowed to stand in the state of some inclining, so that the panel per se is necessary to have a given level of self-supporting properties.